Electrodeposition processes are used in several industries including metal finishing, semiconductor, printed circuit board, and solar industries in order to deposit metal or produce products with desired properties. Electrolytes used for metal deposition processes usually include metal salt (in an amount approx. greater than 1 g/L), a conductive component (e.g., salts, acids, bases, or combinations thereof), pH adjustors and/or buffering agents, and chelating agents. Additionally, electrolytes can include micro-quantities (i.e., less than 1 g/L) of surface active organic additives. The surface organic additives can, for example, modify grain structure, modify grain mechanical properties, provide uniformity of deposits, and provide additional targeted characteristics. In particular, the semiconductor industry has utilized electrodeposited copper as universal interconnect materials for deposits of varying scales, for example, ranging from nanometers (nm) to macro-scales (e.g., inches).
Organic additives can be used in electrodeposition solutions. Organic additives can include, for example, accelerators, brighteners, suppressors and levelers. Accelerators promote defect-free deposits that fill deep or irregular features on the surface to be treated. Accelerators can also be referred to as brighteners. Accelerators and brighteners have a relatively high consumption in electrodeposition processes. Accelerators and brighteners are often used in conjunction with other organic additives, including suppressors and levelers. Suppressors and levelers have relatively low consumption in electrodeposition processes. Suppressors can also be referred to as a carrier, wetter, or leveler. Suppressors can include, for example, polyethylene glycol (PEG). Levelers can include, for example, 8-(4-Dimethylaminophenyl)diazenyl-N,N-diethyl-10-phenylphenazin-10-ium-2-amine chloride (Janus Green B).
For example, accelerators and brighteners can include a sodium salt, such as bis-(3-sulfopropyl) disulfide (SPS, HSO3—CH2—CH2—CH2—S—S—CH2—CH2—CH2—SO3). During the electrodeposition process, SPS is reduced or oxidized to form several breakdown products. One such breakdown product is 3-mercaptopropyl sulfonate (MPS or MPSA, HSO3—CH2—CH2—CH2—SH). For reference, the chemical structures of SPS and MPS are provided in FIG. 1. The breakdown of SPS to MPS generally proceeds according to Formula 1, below:SPS++2H++2e−⇄2 MPS  (Formula 1)
Additionally, several other reactions can occur in parallel, as SPS and MPS degrade into other breakdown products. Such breakdown products included mono-ox-SPS, di-ox-SPS, mono-ox-MPS, di-ox-MPS, and propane disulfonic acid (PDS) via additional oxidation and reduction reactions or hydrolysis. A schematic of these reactions is provided in FIG. 2. Additional description of reactions involving SPS and its breakdown products is provided in Igor Volov, 2013, Copper and Copper Alloys: Studies of Additives, Columbia University Academic Commons, available at http://hdl.handle.net/10022/AC:P:15408, which is incorporated by reference herein. Additional description on the chemistry of additives is provided in Vereecken, P. M., et al., The Chemistry of Additives in Damascene Copper Plating, IBM J. Res. & Dev., Vol. 49 No. 1, pages 3-18, January 2005, which is incorporated by reference herein.
A metal electrodeposition process can include an electrodeposition solution including a metal salt and one or more organic additives. The metal salt included in the electrodeposition solution can be quantitatively utilized during the deposition process (e.g., Me(solution)→Me deposit)). However, utilization of the one or more organic additives included in the electrodeposition solution can be relatively difficult to quantify. For example, the one or more organic additives can be reduced and/or oxidized, cleaved, polymerized and/or codeposited, or removed by drag-out. Drag-out is provided in electrodeposition processes which include sequential dipping of a part into multiple solutions. In electrodeposition processes, an electrodeposition step can be proceeded and followed by a cleaning and surface preparation step. As the part is lifted from a process container, solution is carried with the part. Thus, for example, a part will provide a portion of preceding additive solution and remove a portion of electrodeposition solution including an organic additive resulting in a “carry-over” process or drag-out.
Strategies for process metrology strategy include, for example, monitoring of organic additives and breakdown products of the organic additives. Therefrom, a replenishment dose for the organic additive can be calculated and a lifetime of the electrodeposition solution can be determined. In some processes, “metal turnover” can be used as an indicator of age for an electrodeposition solution (e.g., a total amount of metal added over a lifetime of the solution/initial amount of metal in the solution). The total amount of metal added can be calculated as a total metal dose. The process can be used for an operating condition in which the process tank is replenished over its lifetime and then drained. In another process, “bleed and feed” can be used in which a portion of the solution is removed and replaced with a fresh solution (e.g., daily or more frequently). An age of an electrodeposition solution used in a “bleed and feed” process may be relative difficult to determine, for example, if the “bleed and feed” process occurs on a continuous basis.
Degradation of an organic additive can be characterized through multiple methods for determining a concentration of specific individual breakdown products of the organic additive. Therefore, there is a need for an assessment of additive turnover in solutions. For example, a process of measuring total organic carbon (TOC) can be used. The method includes measuring total carbon remaining in solution to determine the age of the solution. Thus, the method fails to measure carbon, for example, that is codeposited, oxidized into carbon dioxide (CO2), or removed by drag-out. Further, industries often provide organic acids and metal organic salts as a large component of electrodeposition solutions, e.g., methanesuflonic (MSA) CH3—SO3 (−) as a substitute for sulfate SO4 (2−). TOC processes monitor large levels of MSA and are not able to detect lower level changes of concentrations of accumulated organics (e.g., changes in ppm). Additionally, when an organometallic component is not used in the electrodeposition solution, carbon load can be unevenly distributed, for example, with a suppressor contributing at least 90% of the total carbon. Thus, TOC processes monitor total accumulation of the suppressor, however, are not able to monitor the accumulation of other micro components in the electrodeposition solution. Other methods describe monitoring the concentrations of inorganic counterions of organic additives in solution to determine and monitor the age of the solution (e.g., measuring sulfate concentration in CuSO4 metal salt of an electrodeposition solution).
However, these techniques can be insufficient in determining an age of a solution to effectively control additive turnover as prior methods provide several methods targeting individual breakdown products of organic additives. Thus, there remains a need for methods for more accurate and comprehensive measurement and control of additive turnover in a solution.